Igniter for Downhole Use Having Flame Control

ABSTRACT

An igniter initiates combustion in an amount of explosive that is downhole and adjacent the igniter. The igniter includes an amount of combustible material and a resistive igniter element disposed on a side of the combustible material that faces the amount of explosive. Applying a designated amount of electricity to the resistive igniter element generates sufficient heat to ignite the combustible material. Strategically initiating ignition adjacent the amount of explosive generates a flame front that travels away from the explosive, which in turn directs a flame against the explosive substantially the entire time the combustible material burns.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present disclosure relates in general to an igniter for igniting an explosive downhole, and which includes a propellant with a point of combustion adjacent the explosive.

2. Description of Prior Art

Explosives are sometimes used during downhole operations for the exploration and production of subterranean hydrocarbons. Perforating systems typically have shaped charges equipped with high explosive for generating a metal jet that pierces a wellbore wall to create perforations into the formation surrounding the wellbore. The shaped charges are disposed axially along the length of perforating guns that make up a perforating system. A detonation cord is usually placed adjacent each shaped charge, through which a detonation wave travels for initiating detonation of the high explosive.

Packers and plugs are typically elastomeric bladder like elements that expand radially outward from a mandrel or downhole tool and into sealing contact with an inner surface of a wellbore wall. The sealing contact creates a pressure/flow barrier in the annulus between the tool and wellbore wall for isolating a designated portion of the wellbore. Some downhole packers or plugs are set with explosives that are included with the downhole tool.

Igniters are usually included downhole for initiating combustion or detonation in a propellant, the detonating cord, or explosives. Typically, an igniter includes a cartridge, combustible material in the cartridge, and a resistive heating element inserted into combustible material. Electricity is supplied to the heating element via an electrode which ignites the combustible material. A flame exits the cartridge and is directed to an amount of combustible or explosive material adjacent the detonation cord or combustible material for ultimately detonating the shaped charges or setting the packer/plug.

SUMMARY OF THE INVENTION

Disclosed herein is an example of an igniter, and a method, for initiating combustion and/or detonation of an explosive downhole. One example of the igniter includes a housing having an opening proximate the explosive, a combustible material in the housing, an igniter assembly in the opening and that is in thermal contact with the combustible material, so that when the igniter element is heated to a temperature that initiates combustion of the combustible material, a flame is generated in the housing which is directed to the explosive and that ignites the explosive. The igniter element can be made of an elongated resistive element which is made from a conductive material that is heated when current flows through the resistive element. The resistive element can be mounted on a printed circuit board. An electrode can be included in the housing for electrically coupling the resistive element with an electrical source. The explosive can be part of a perforating system or can be used for setting a packer in a wellbore.

An alternative igniter for igniting an explosive downhole includes a housing having an opening, a propellant in the housing, an electrode inserted into the propellant and in electrical communication with a source of electricity, a resistive element in electrical communication with the electrode and in thermal contact with a surface of the propellant that is proximate the explosive, so that when electricity is supplied to the electrode from the source of electricity, current flows through the resistive element and heats the resistive element to a temperature that ignites the propellant, that in turn ignites the explosive. The resistive element may include an elongated electrically conductive member that is arranged in a helical configuration defined by a series of loops radially spaced away from one another. In this example, spacing between adjacent loops can be greater proximate an axis of the helical configuration. The resistive element may optionally be mounted on a printed circuit board that is set in the opening of the housing. The explosive can be used in a perforating system or for setting a packer.

A method of detonating an explosive downhole is disclosed that includes providing an amount of combustible material in a housing adjacent the explosive, initiating combustion of the combustible material on an end of the combustible material that is proximate the explosive so that a flame front is created in the combustible material that travels away from the explosive that in turn generates a flame that is directed from the housing to the explosive and which ignites the explosive. The method may further include flowing current through a resistive element that is in thermal contact with the end of the combustible material proximate the explosive, wherein the resistive element becomes heated and initiates combustion of the combustible material. The explosive can be used for initiating detonation of shaped charges that create subterranean perforations, or for setting a packer in a wellbore.

BRIEF DESCRIPTION OF DRAWINGS

Some of the features and benefits of the present invention having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a side sectional view of an example of an igniter in accordance with the present invention.

FIG. 2 is an axial sectional view of the igniter of FIG. 1 taken along lines 2-2 and in accordance with the present invention.

FIG. 3 is a side sectional view of an example of operation of the igniter of FIG. 1 and in accordance with the present invention.

FIG. 4 is a side sectional view of an example of a perforating system using the igniter of FIG. 1 and in accordance with the present invention.

FIG. 5 is a side sectional view of an example of setting a packer using the igniter of FIG. 1 and in accordance with the present invention.

While the invention will be described in connection with the preferred embodiments, it will be understood that it is not intended to limit the invention to that embodiment. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the invention as defined by the appended claims.

DETAILED DESCRIPTION OF INVENTION

The method and system of the present disclosure will now be described more fully hereinafter with reference to the accompanying drawings in which embodiments are shown. The method and system of the present disclosure may be in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey its scope to those skilled in the art. Like numbers refer to like elements throughout. In an embodiment, usage of the term about includes +/−5% of the cited magnitude.

It is to be further understood that the scope of the present disclosure is not limited to the exact details of construction, operation, exact materials, or embodiments shown and described, as modifications and equivalents will be apparent to one skilled in the art. In the drawings and specification, there have been disclosed illustrative embodiments and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation.

Shown in FIG. 1 is a side sectional view of an example of an igniter 10 which has an elongate housing 12 and a body 14 mounted on an upper end of housing 12. A propellant 16 is shown disposed within housing 12. Examples of propellant 16 include any energetic material that can be burned, combusted, or otherwise decomposed, and which generates energy when burned, combusted, or decomposed. An elongate electrode 18 shown inserted through the body 14 and into the housing 12 and is set within propellant 16. In the example of FIG. 1, electrode 18 is an electrically conducting element, an insulator 20 shown disposed between the electrode 18 and housing 14 to block electrical communication between electrode 18 and housing 14. A lead 22 connects to an end of electrode 18 that protrudes outward from a side of the body 14 distal from housing 12 and which provides selective electrical communication between electrode 18 and an electrical source 23. Examples of an electrical source include a battery, compositor, generator, and the like.

Shown set in housing 12 and on an end of propellant 16 distal from body 14 is an igniter assembly 24 for initiating combustion of propellant 16. In the embodiment shown, igniter assembly 24 is disposed in an opening 25 of the housing 12 that is distal from body 12. Igniter assembly 24 includes a printed circuit board 26 and a resistive element 28 mounted on a surface of printed circuit board 26 facing propellant 16. Further in the example of FIG. 1, the igniter assembly 24 is shown between propellant 16 and an explosive 30 adjacent an end of housing 12 distal from body 14. The explosive 30 includes an amount of explosive material which is packed within a housing 32 that is substantially coaxial with housing 12. Examples of explosive material include any high explosive, such as octogen (HMX), cyclonite (RDX), hexanitrostilbene HNS, to name a few; any low explosive, and any other material that can detonate when initiated.

Referring now to FIG. 2, an axial sectional view is provided that is taken along lines 2-2 of FIG. 1 and which gives a plan view of printed circuit board 26. As shown, resistive element 28 is made from an elongate and electrically conductive resistive lead 34. In the example, resistive lead 34 is arranged in a helical shape whose origin is proximate the axis A_(x) of igniter 10 (FIG. 1). From the origin, the resistive lead 34 spirals radially outward towards the outer periphery of printed circuit board 26. Also shown in FIG. 1 is that electrode 18 rests on the resistive lead 34 so that the resistive element 28 and electrode 18 are in electrical communication. Referring back to FIG. 2, an optional resistive electrode 36 is provided on an end of resistive lead 34 proximate axis A_(x), electrode 36 is a planar element made from a conductive material. Electrode 36 defines a larger cross section than the lead 34 so that communication between electrode 18 and resistive element 28 is optimized. Alternatively, the end of resistive lead 34 opposite from resistive electrode 36 attaches to a ground G, which as shown in FIG. 1 may include housing 12.

One example of operation of igniter 10 is shown in side sectional view in FIG. 3 wherein the amount of electricity from electrical source 23 is supplied to electrode via lead 22. The electricity in electrode 18 generates a flow of current through resistive lead 34 (FIG. 2) which in turn heats resistive lead 34 to a designated temperature that is above the ignition temperature for the propellant 16. As thermal energy from resistive lead 34 transfers to the propellant 16, the resistive lead 34 and propellant are in thermal contact. By applying sufficient thermal energy to propellant 16, the propellant 16 begins to combust and generates a flame front 38. Arrows represent travel of the flame front 38 in a direction away from explosive 30. As the flame front 38 moves away from the opening 25 of the housing 12, a flame discharge 40 is created that is directed into the explosive 30. The flame discharge 40 ignites explosive 30 to form an ignition/detonation front 42, and which is shown travelling through the explosive 30. One of the advantages of the present disclosure is that by igniting propellant 16 at an end, rather than in its middle, the flame discharge 40 is sustained and directed onto explosive 30 substantially during the entire time the propellant 16 is being combusted. As such, greater likelihood exists that the ignition/detonation front 42 will be created within explosive 30 and carry out its intended operation. Further in the example of FIG. 3, igniter assembly 24 (shown in phantom view) basically disintegrates during generation of the flame discharge 40. Alternatively, the electrical circuit made up of the resistive lead 34 and electrode 18 can be all within electrode 18 so that connection to housing 12 is unnecessary.

Referring now to FIG. 4, one example of using the igniter 10 in conjunction with a perforating operation is shown in a side sectional view. In this example a perforating system 44 is shown deployed in a wellbore 45 where the igniter 10 is explosively coupled with an upper end of a detonation cord 46 that extends the length of the perforating system 44. Shaped charges 48 are provided in system 44 that are detonated by a pressure wave within detonation cord 46. Detonating the shaped charges 48 form metal jets that create perforations 50 radially outward into a formation 52 surrounding wellbore 45. A wireline 54 provides the electrical signal to the igniter 10 from electrical source 23 (FIG. 1). Wireline 52 is shown threaded through a wellhead assembly 56 that is mounted on the opening of wellbore 45. A surface truck 58, which may contain the electrical source 23, provides control of the perforating system 44 as well as a means for deploying the system 44.

Alternatively, igniter 10 is used in conjunction with a downhole tool 60 for setting a packer (or plug) 62 which projects radially outward from tool 60 and into sealing engagement with the walls of wellbore 45. Also in the example of FIG. 5, the tool 60 is deployed on wireline 54 that strings through wellhead assembly 56 from surface truck 58. As is known, igniter provides the ignition source for igniting an explosive that is used in setting packer 62.

In an example, the explosive material making up the explosive 30 detonates after being initiated, wherein a definition of detonation describes a reaction that can propagate through the material being detonated at the sound speed of the material. In a further example, detonation describes a reaction or decomposition of an explosive that, typically in response to a shock wave or heat, forms a high pressure/temperature wave. Example velocities of the high pressure/temperature wave can range from 1000 m/s to in excess of 9000 m/s. In another example, the explosive 30 can deflagrate, wherein a definition of deflagration describes a rapid auto-combustion of a material, such as an explosive. Generally, explosives that detonate are referred to as high explosives and explosives that deflagrate are referred to as low explosives. Alternate embodiments exist wherein the explosive 30 includes a propellant that combusts (or is otherwise combustible), or is replaced with a propellant. In an example, combustion describes an exothermic reaction of a material that can produce an oxide.

The present invention described herein, therefore, is well adapted to carry out the objects and attain the ends and advantages mentioned, as well as others inherent therein. While a presently preferred embodiment of the invention has been given for purposes of disclosure, numerous changes exist in the details of procedures for accomplishing the desired results. These and other similar modifications will readily suggest themselves to those skilled in the art, and are intended to be encompassed within the spirit of the present invention disclosed herein and the scope of the appended claims. 

What is claimed is:
 1. An igniter for igniting an explosive downhole comprising: a housing having an opening proximate the explosive; a pyrotechnic material in the housing; an igniter assembly in the opening and that is in thermal contact with the pyrotechnic material, so that when the igniter element is heated to a temperature that initiates combustion of the combustible material, a flame is generated in the housing which is directed to the explosive and that ignites the explosive.
 2. The igniter of claim 1, wherein the igniter element comprises an elongated resistive element which is made from a conductive material that is heated when current flows through the resistive element.
 3. The igniter of claim 2, wherein the resistive element is mounted on a printed circuit board.
 4. The igniter of claim 1, further comprising an electrode in the housing for electrically coupling the igniter assembly with an electrical source.
 5. The igniter of claim 1, wherein the explosive is part of a perforating system.
 6. The igniter of claim 1, wherein the explosive is for setting a packer in a wellbore.
 7. An igniter for igniting an explosive downhole comprising: a housing having an opening; a propellant in the housing; an electrode inserted into the propellant and in electrical communication with a source of electricity; a resistive element in electrical communication with the electrode and in thermal contact with a surface of the propellant that is proximate the explosive, so that when electricity is supplied to the electrode from the source of electricity, current flows through the resistive element and heats the resistive element to a temperature that ignites the propellant, that in turn ignites the explosive.
 8. The igniter of claim 7, wherein the resistive element comprises an elongated electrically conductive member that is arranged in a helical configuration defined by a series of loops radially spaced away from one another.
 9. The igniter of claim 8, wherein spacing between adjacent loops is greater proximate an axis of the helical configuration.
 10. The igniter of claim 7, wherein the resistive element is mounted on a printed circuit board that is set in the opening of the housing.
 11. The igniter of claim 7, wherein the explosive is selected from the list consisting of an explosive used in a perforating system and an explosive used for setting a packer.
 12. A method of detonating an explosive downhole comprising: providing an amount of combustible material in a housing adjacent the explosive; initiating combustion of the combustible material on an end of the combustible material that is proximate the explosive so that a flame front is created in the combustible material that travels away from the explosive that in turn generates a flame that is directed from the housing to the explosive and which ignites the explosive.
 13. The method of claim 12, further comprising flowing current through a resistive element that is in thermal contact with the end of the combustible material proximate the explosive, wherein the resistive element becomes heated and initiates combustion of the combustible material.
 14. The method of claim 12, wherein the explosive is used for initiating detonation of shaped charges that create subterranean perforations.
 15. The method of claim 12, wherein the explosive is used for setting a packer in a wellbore. 